<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <style>
      html {
        filter: grayscale(1);
        /* 灰阶滤镜 */
      }
    </style>
  </body>
</html>
